Microelectronic devices or features are typically formed in or on workpieces (including semiconductor wafers) by selectively removing material from the wafer and filling in the resulting openings with insulative, semiconductive and/or conductive materials. One typical process includes depositing a layer of radiation-sensitive photoresist material on the wafer, then positioning a patterned mask or reticle over the photoresist layer, and then exposing the masked photoresist layer to a selected radiation. The wafer is then exposed to a developer, such as an aqueous base liquid or a solvent. This process is generally known as photolithography.
In one photolithography process, the photoresist layer is initially generally soluble in the developer, and the portions of the photoresist layer exposed to the radiation through patterned openings in the mask change from being generally soluble to being generally resistant to the developer (e.g., so as to have low solubility). Alternatively, the photoresist layer can be initially generally insoluble in the developer, and the portions of the photoresist layer exposed to the radiation through the openings in the mask become more soluble. In either case, the portions of the photoresist layer that are resistant to the developer remain on the wafer, and the rest of the photoresist layer is removed by the developer to expose the wafer material below.
The wafer is then subjected to etching or metal deposition processes. In an etching process, the etchant removes exposed material, but not material protected beneath the remaining portions of the photoresist layer. Accordingly, the etchant creates a pattern of openings (such as grooves, channels, or holes) in the wafer material or in materials deposited on the wafer. These openings can be filled with insulative, conductive, or semiconductive materials to build layers of microelectronic features on the wafer. The wafer is then singulated to form individual chips, which are used in a wide variety of electronic products.
The semiconductor manufacturing industry continuously strives to make ever smaller microelectronic devices and features. Making these features smaller allows for smaller and lighter electronic products, reduces the electrical power required to operate them, and can also reduce manufacturing costs. These efforts have allowed electronic products, such as cell phones and other wireless devices, computers, PDA's etc. to be smaller and lighter, with improved battery life, and greater functionality. As the size of the microelectronic features formed in the wafer decreases (for example, to reduce the size of the chips placed in electronic devices), the size of the features formed in the photoresist layer must also decrease.
Photolithography in the semiconductor industry has traditionally used light projected through a lens system onto a substrate, such as a silicon wafer. Air or another gas fills the gap or space between the lens and the substrate. However, the air or gas between the lens, or the last lens element, and the substrate, limits the maximum resolution of the lens system. This in turn largely prevents the photolithography process from making microelectronic devices or features below a certain size. To overcome this limitation, immersion lithography machines have been proposed. These immersion stepper or scanner machines perform optical lithography with a liquid between the lens and the substrate. Since liquids, such as water, have a higher index of refraction than air or gases, better resolution can be achieved. This allows smaller devices to be manufactured.
The lens in an immersion scanner is advantageously maintained wet or immersed between uses. In current immersion scanners, a wetting unit is raised up to the lens, when the scanner is idle. The wetting unit has a set of seals to help to confine the liquid around the lens. These seals are generally different from the seal techniques used to confine the liquid around the lens when the scanner is in use. Consequently, the need for the wetting unit adds to the cost and complexity of the scanner.
Many specific details are set forth in the following discussion and in FIGS. 1-5 to provide a thorough description. One skilled in the art, however, will understand that the invention may have additional embodiments, and that the invention may be practiced without several of the details and elements described below. The invention may reside as well in components, subcombinations or subsystems of the apparatus and methods described.